Ship signature modifier

ABSTRACT

A unique system of disposition-controlled, water-filled, fabric bags is  sended from and towed beneath a ship to effect the modification of the inherent water pressure signature thereof and thus prevent detonation of a marine mine programmed to be exploded thereby.

The invention described herein may be manufactured and used by or forthe Government of the United States of America for governmental purposeswithout the payment of any royalties thereon or therefor.

The present invention relates generally to marine mine defense systemsand, in particular, is a system for disguising the pressure signature ofa ship in such manner as to prevent detonation of a marine mine that isprogrammed to be exploded thereby as it passes thereover.

Heretofore, conventional mine sweeping operations have been applied topressure responsive marine mines in an attempt to provide safe passagefor ships or other marine vehicles, as they travel along their intendedcourse. For example, preceding the traverse of any given body of waterby a ship requiring protection from pressure responsive mines, a varietyof marine mine sweeping vehicles may be driven thereover which have beenstructurally constructed to produce water pressure signatures thatsimulate those of the real ship or ships to be protected. As a result,any pressure responsive marine mines that happen to be located withinthe influence thereof are detonated thereby and thus rendered harmlessto any real ship passing over that particular location at somesubsequent time. Although satisfactory for some purposes, such methodand means for neutralizing or destroying marine pressure mines toprovide safe passage for ships usually leaves a great deal to bedesired. In the first place, such mine sweeping operations must beeffected prior to the arrival of the real ship or ships to be protected.Hence, an enemy who may be cognizant of the mine sweeping operationwould be forewarned of the coming of a ship or other marine vehicle thatmost likely would be detrimental to them, and they could prepare to takeother defensive or offensive action against it, which would obviouslyplace it in greater jeopardity than it would be in without suchforewarning. Moreover, in order to provide effective sweeping of suchpressure responsive marine mines, a considerable amount of expensiveminesweeping equipment, manpower, and time is required. Such equipmentmust be constructed, transported to the location involved, and thenoperated either directly or indirectly by trained personnel. Of course,due to the time element involved, the keeping of such minesweepingoperations from coming to the attention of the enemy is highlyimprobable; consequently, such operations are usually hazardous to boththe minesweeping apparatus and the people operating it. Therefore, itmay readily be seen that when the circumstances are such as would allowit, it would definitely be desirable to change the water pressure ofactual ships in such manner that they would not cause the detonation ofpressure responsive marine mine and thereby eliminate the necessity ofpreceding them with minesweeping operations.

The subject invention is an attachment that may be mounted on a ship forthe purpose of changing it water pressure signature, so that it may passover pressure responsive marine mines without being harmed thereby. Itnot only obviates the necessity of prior mine sweeping under somecircumstances, but it is also an improvement over similar devices of theprior art. This is true because, by comparison, it is simple toconstruct, it is rather easy to operate, and it provides protection forships or other marine vehicles at such time when they could not beprotected in any other way. Of course, as an ancillary benefit, it alsoprovides a relatively easy way to vary the water pressure signature of aship for any given purpose, be it military or otherwise.

It is, therefore, an object of this invention to provide an improvedmethod and means for varying the water pressure signature of a ship orother marine vehicle.

Another object of this invention is to provide an improved method andmeans for disguising a ship's water pressure signature.

Still another object of this invention is to provide an improved systemfor increasing the safety of a ship passing through a marine mine fieldcomposed of pressure responsive mines.

A further object of this invention is to provide an improved, easilyinstalled attachment for effectively changing the hull configuration ofa ship or other marine vehicle.

Another object of this invention is to provide a ship water pressuresignature changing attachment that may be adjustably disposed relativeto the hull thereof, in order to optimize its effects for various shipspeeds and water depths.

Another object of this invention is to provide an improved ship waterpressure signature changing method and means that may be manuallyadjusted to provide safe passage of a ship while it is traveling over alarge variety of marine pressure responsive mines.

Another object of this invention is to provide an improved shipsignature disguising means that is easily and economically constructed,stored, maintained, and operated, and which is expendable, should thesituation arise during ship maneuvers which would make it desirable todiscard it at quick notice.

Another object of this invention is to provide an improved method andmeans which, under certain circumstances, substantially obviate thenecessity of sweeping the pressure responsive mines of a marine minefield prior to the passage of a ship or other marine vehicle thereover.

Other objects and many of the attendant advantages will be readilyappreciated as the subject invention becomes better understood byreference to the following detailed description, when considered inconjunction with the accompanying drawings wherein:

FIG. 1 is an elevational view of an exemplary preferred embodiment ofthe system constituting this invention;

FIG. 2 is a bottom view of the exemplary system of FIG. 1;

FIG. 3 is an elevational view of a bag that may be used in the system ofFIGS. 1 and 2;

FIG. 4 is a front view of the bag of FIG. 3; and

FIG. 5 is a graphical representation of hypothetical ship signatureswith and without the subject invention attached thereto.

Referring now to FIG. 1, there is shown a ship 11 which is intended totraverse various and sundry waterways 12 that are mined with programmedpressure responsive marine mines 13 and 14 that may be laying on seafloor 15 or tethered from an anchor 16, respectively.

It should be understood that ship 11 is shown in this particularinstance in order to simplify the disclosure thereof, but that thesubject invention is also susceptible to being installed on any othersuitable marine vehicle, if so desired. Obviously, so doing would bewell within the purview of one skilled in the art having the benefit ofthe teachings presented herewith.

A winch 17 capable of paying out and reeling in a tow cable 18 ismounted on the deck or other appropriate location of ship 11. Cable 18is suspended from winch 17 and is threaded over a predisposed cableretention stop or bearing 19, preferably located at the lowest bowextremity of ship 11. Bearing 19 may have any suitable structuralconfiguration--such as, for example, an appropriate hookconfiguration--which will enable one or more cables to slide thereoverwithout being released therefrom and still allow the remainder of theinvention to be withdrawn from the water when necessary.

Cable 18 extends rearwardly under ship 11 and is connected by means of abridle 21 to a fabric bag 22. Attached to cable 18 may be a diverter 23and a depressor 24, which are used to apply forces thereto in suchmanner as to properly position bag 22 under or substantially under ship11, as it is being pulled along underwater thereby.

Bag 22 is an unusual type bag. Actually, it is somewhat like a wind sockand could perhaps be considered as being a water sock. Suffice to say atthis time, it is preferably made of fabric and allows water to flow intoit to maintain an inflated shape, as it is being pulled through thewater. Further detailed thereof will be given subsequently inconjunction with the disclosure of the device of FIG. 3.

As depicted in the elevational view of FIG. 1, only one bag 22 andtowing cable 18 are seen as being used; however, it should be understoodthat any number of bags and towing cables may be combined withoutviolating the scope of the system constituting the subject invention.For example, three such bags and tow cables are illustrated in FIG. 2.Of course, when FIG. 2 is considered as the bottom view of FIG. 1, thenthe system of FIG. 1 contains said three bags and towing cables, eventhrough only one bag and one towing cable are visible therein.

Assuming for the sake of disclosing a simple preferred embodiment of theinvention that FIG. 2 is a bottom view of FIG. 1, then tow cable 18,bridle 21, bag 22, and diverter 23 are also incorporated in its system.In addition, another tow cable 25, bridle 26, and bag 27 are includedtherein, and still another tow cable 28, bridle 29, and bag 30 are,likewise, included therein. And since it is desirable that bags 22 and30 be outwardly disposed from center bag 27, the aforementioned diverter23 and another diverter 31 are appropriately attached to cables 18 and28, respectively, so as to apply the proper vector forces to bags 22 and30 to position them accordingly.

Depending on the ship hull involved and the pressure signature wanted,cables 18, 25, and 28 may be paid out by winch 17 to position bags 22,27, and 30 at whatever distance behind the bow and at whatever distancebelow the hull of ship 11 as is necessary during any given operationalcircumstances. The latter parameter would also be controlled to aconsiderable extent by the aforementioned depressor 24, as well as apair of depressors 32 and 33, respectively connected to tow cables 18,25, and 28.

Again, it should be understood that any number or combination of bagsand associated disposition control apparatus may be employed that willfacilitate provided protection to ship 11. Hence, for instance, bag 27and its associated apparatus could be the entire system or could bedeleted from the system. Or, in the alternative, either or both of bags22 and 30 could be deleted from the system, depending on the waterpressure signature desired for any given operational circumstances.

FIGS. 3 and 4 disclose representative side and end views, respectively,of a bag 35 that may be used as the aforesaid bags 22, 27, and 30. It ispreferably made of fabric, and included therein is a stiffner 36 whichmay take the form of a roll of cloth, a plastic ring, or the like. Thepurpose of stiffner 36, of course, is to hold the front end 37 open insuch manner as to enable it to scoop water into the remainder of thebag. The fabric walls 38 are shaped for best hydrodynamic performance,and the rear end 39 thereof may have a small diameter opening 40 locatedtherein. However, it should be understood that said rear end opening isnot essential to the functioning of the bag, and, thus, may beconsidered as being optional. In the event opening 40 is incorporated inthe aft end 39 of bag 35, it will ordinarily releave some of thehydrodynamic stresses occurring therein, while it is being pulledthrough the water; furthermore, it will usually facilitate withdrawingthe bag from the water after operations are completed, because it actsas a drain hole through which the water is removed therefrom.

In this particular disclosure, the thickness of wall 38 is somewhatexaggerated; however, any suitable thickness that provides the properoperation may be used.

A bridle 41 is depicted as being attached to the front end 37 at fourplaces 42, 43, 44, and 45, but any other configuration that providesuniformity of towing pull and stability of the bag may be employed. Atowing cable 46, similar to cable 18 above, is connected at a suitablecontrol point 47 on said bridle 41.

It was suggested above that bag 35 preferably be made of fabric; on theother hand, it should be understood that the invention is not intendedto be limited thereto. For example, bag 35 may be made of any suitableflexible material, such as fiberglass, paper, cloth, plastic, canvas, orthe like. As a general rule, it is also preferable that said bagmaterial be of a non-magnetic type.

In like manner, the aforementioned tow cables 18, 25, and 28 shouldpreferably be made of non-magnetic materials, so as not to adverselyaffect the safety of the ship with respect to other marine mines--suchas, for instance, magnetic responsive marine mines. Likewise, any andall positioning apparatus, such as the aforesaid diverters anddepressors, are preferably non-magnetic. However, in the event magneticmines need not be taken into consideration or the subject system is partof an overall ship magnetic system, any or all of the components thereofmay be made of magnetic materials or any other materials suitable forsuch purpose.

FIG. 5 is incorporated herewith in order to illustrate a theoreticalcomparison between the signature of a ship with and without the subjectinvention attached thereto. Solid line curve 48 illustrates a typicalwater pressure signature of a ship or the like without the inventionattached thereto, and dashed line curve 49 depicts a hypothetical waterpressure signature which might occur, if the same ship has the inventionattached thereto. Obviously, the difference in pressure signatures isconsiderable and, consequently, the changed pressure signature, effectedby the invention, may be employed to disguise the real or inherentsignature of the ship.

The operation of the invention will now be discussed briefly inconjunction with all of the figures of the drawing.

As a ship travels through the water on its desired course, the pressureof the water beneath it varies, depending on the length, geometricalconfiguration, weight, and speed thereof. Such a variation is defined inthe art as being the signature of the ship. Obviously, such signature isdifferent for each ship design and may, from time to time, vary for thesame ship, in the event its loading, speed, and other conditions arevaried. Nevertheless, many ships (or other marine vehicles) aresufficiently similar in signature that marine mines have been designedto be detonated in response thereto, when it is desired to sink orotherwise disable them during war time. On the other hand, it mayreadily be seen that mines may also be programmed not to explode inresponse to certain ship signatures and to explode in response toothers. This invention has, therefore, been made in an attempt todeceive the enemy mines that would otherwise destroy or disable friendlyships, so as to allow their safe passage through a mine field composedthereof. Of course, it may also be used indirectly with U.S. mines todestroy enemy ships having a signature somewhat similar to U.S. shipsnot incorporating the invention, while allowing safe passage for U.Sships which have the system constituting the subject invention installedthereon.

The particular water pressure signature effected by this invention iscontingent upon the number and disposition of bags hung immediatelyunder and/or sidewardly and downwardly extending from any given ship.Hence, a different signature would result if only one bag is usedinstead of three, as is shown in FIG. 2. Moreover, a different signaturewould be effected if only two of the bags were used, regardless of whichtwo were selected. Furthermore, the distance aft of the ship's bow andthe distance beneath the ship's hull at which the bag or bags arepositioned make a difference in the signature produced thereby. Ofcourse, the particular arrangement selected would depend on the shipinvolved and its operational circumstances. In any event, the properemployment of any number of bags of predetermined size and shape(perhaps even more than three, if necessary) changes the water pressuresignature of any given ship.

Because it is not uncommon to tow various and sundry devices, bags,etc., fore or aft of ships performing functions other than thoseherewith described, such things should be distinguished from the subjectinvention. For example, it is well known to tow large wind sock-likebags under the water behind a marine vehicle for the purpose ofsimulating a ship signature and thus effecting the detonation ofpressure responsive mines. In those instances, however, the purposethereof is to explode said mines, rather than to provide safe passagethereover, as is the case with the subject system. Furthermore, in suchmine sweeping operations, it should be noted that the bags or otherdevices are towed at one or more positions that are relatively remotefrom the towing vessel, and, in fact, the only reason a towing vessel ispresent at all is to provide a tractor means to move the towed bags orother devices through the water. The subject invention, on the otherhand, requires that the bag or bags be towed within the immediatevicinity of the underside of the ship, so that its inherent signaturewill be modified sufficiently to prevent the detonation of any pressureresponsive marine mine designed to explode in response to a similarnormal ship signature. This difference is exceedingly important, becauseit enables the subject invention to meet the paramount test forinvention, viz., that it is a new and useful system that produces a newand useful result.

During actual operation, as the ship travels along its desired course,the bag or bags suspended thereunder fill with water and thus produce aphysical body or bodies which effectively combine with the ship's hullto produce a new overall pressure signature. Because the bag or bags areconstructed with open front ends, water flows into them and inflatesthem to produce semi-flexible, relatively large volume bodies whicheffectively displace an amount of water under the ship that issubstantially equal to the total volume thereof. It is this new totaleffective volume of "displaced" water that combines with the displacedwater volume of the ship's hull to effectively produce a different hullconfiguration that generates a new pressure signature for any givenship.

When not in use, being made of fabric and flexible cables, etc., theinvention is portable and easily stored until such time as it is neededto provide safe passage for the ship. And when such occasion does arise,it is readily installed under the ship by operating which 17 to pay outthe tow cables in such manner that the bags and associated positioncontrol accessories will effectively be towed from the aforesaidpredetermined cable retaining bearing point 19, located substantially atthe lowest bow point of the ship.

As shown in FIG. 5, water pressure is plotted against the distance overwhich said pressure is measured as a ship passes by. Such water pressureis measured at some location--usually on or near the sea floor--wherepressure responsive marine mines are ordinarily located during war time.The distance over which it is measured is, of course, contingent on thesize of the ships involved; but in FIG. 5, the terms B and Srespectively refer to the bow and stern locations of a hypothetical shipof any size and are employed therein to illustrate how signatures 48 and49, the inherent and modified signatures thereof, relate thereto.Obviously, it is the difference between the pressure of curve 48 and thepressure of curve 49 which facilitates the safe passage of any givenship or other marine vehicle over any marine mines 13 and 16 that areprogrammed to explode in response to the inherent signature 48 thereof.

In view of the foregoing, it ostensively may be seen that the subjectinvention provides a unique safety feature for ships traveling overpressure responsive marine mines and, hence, an advance in the art iseffected thereby.

What is claimed is:
 1. A marine vehicle water pressure signaturemodification system comprising in combination:hollow, flexible,water-inflatable means capable of being inflated to a predeterminedvolumetric configuration by water being forced into the hollow thereof,as it is being towed therein; a marine vehicle having a predeterminedhull configuration; and means effectively connected between said marinevehicle and the aforesaid hollow, flexible, water-inflatable means forthe towing thereof at a predetermined water depth from the bottom ofsaid marine vehicle and at a given intermediate position between the bowand stern thereof.
 2. The system of claim 1 further characterized by anexit hole located in the aft end of said hollow, flexible,waterinflatable means capable of being inflated to a predeterminedvolumetric configuration by water being forced into the hollow thereof,as it is being towed therein, with the size of said exit hole beingsmaller than the size of the entrance through which said water passes asit is being forced into the aforesaid hollow thereof.
 3. The system ofclaim 1 wherein said marine vehicle having a predetermined hullconfiguration is a ship.
 4. The system of claim 1 wherein said hollow,flexible, water-inflatable means capable of being inflated to apredetermined volumetric configuration by water being forced into thehollow thereof, as it is being towed therein comprises an elongated baghaving an open front end and a closed aft end.
 5. The system of claim 1wherein said hollow, flexible, water-inflatable means capable of beinginflated to a predetermined volumetric configuration of water beingforced into the hollow thereof, as it is being towed thereincomprises:an elongated bag having a longitudinal axis of revolution; apassageway extending through said elongated bag along the longitudinalaxis of revolution thereof, with the forward entrance thereof having alarger diameter than the rearward exit thereof; and means mounted incontiguous disposition with the forward entrance of said passageway forthe maintenance thereof in a substantially open configuration.
 6. Thesystem of claim 1 wherein said hollow, flexible, water-inflatable meanscapable of being inflated to a predetermined volumetric configuration ofwater being forced into the hollow thereof, as it is being towed thereincomprises a plurality of bags, each of which has an open front end and aclosed aft end.
 7. The system of claim 1 wherein said hollow, flexible,water-inflatable means capable of being inflated to a predeterminedvolumetric configuration by water being forced into the hollow thereofas it is being towed therein comprises a plurality of elongated bags,each of which includes:a longitudinal axis of revolution; a passagewayextending therethrough along the longitudinal axis of revolutionthereof, with the forward entrance of said tapered passageway having alarger diameter than the rearward exit thereof; and means mounted incontiguous disposition with the forward entrance of said passageway forthe maintenance thereof in a substantially open configuration.
 8. Thesystem of claim 1 wherein said means effectively connected between saidmarine vehicle and the aforesaid hollow, flexible, water-inflatablemeans for the towing thereof at a predetermined water depth from thebottom of said marine vehicle and at a given intermediate positionbetween the bow and stern thereof comprises:a tow cable; and meanseffectively connected to said tow cable for the urging thereof toward apredetermined position as a result of said tow cable being pulledthrough the water by the aforesaid marine vehicle.
 9. The system ofclaim 8 further characterized by a winch connected between the forwardend of said tow cable and said marine vehicle.
 10. The system of claim 8further characterized by a bridle connected between the aft end of saidtow cable and the forward end of the aforesaid hollow, flexible,water-inflatable means.
 11. The system of claim 1 wherein said meanseffectively connected between said marine vehicle and the aforesaidhollow, flexible, water-inflatable means for the towing thereof at apredetermined water depth from the bottom of said marine vehicle and ata given position between the bow and stern thereof comprises:a pluralityof tow cables; and means effectively connected to each of said towcables for the respective urging thereof toward predetermined positionsas a result of said tow cables being pulled through the water by theaforesaid marine vehicle.
 12. The system of claim 11 furthercharacterized by a winch connected between the forward ends of saidplurality of tow cables and said marine vehicle.
 13. The system of claim11 further characterized by a plurality of bridles connected between theaft ends of said plurality of tow cables and the forward ends of theaforesaid hollow, flexible, water-inflatable means, respectively.
 14. Amethod of modifying the water pressure signature of a marine vehiclecomprising the steps of:disposing at least one open-ended, elongated,flexible bag, having a forward open end that is larger than the aft openend thereof, substantially under the marine vehicle the water pressuresignature of which is to be modified, with the longitudinal axis thereofsubstantially parallel to the direction of travel of said vehicle;driving the marine vehicle, the water pressure signature of which is tobe modified, along a given course; and towing said bag from apredetermined control position on said marine vehicle in such mannerthat it fills and inflates with water as said water flows therethroughand substantially maintains the aforesaid disposition in said inflatedcondition as said marine vehicle is driven along its given course.